Serine Protease Inhibitors
The serine protease plasmin, which is a normal blood constituent, has been shown to activate endogenous immunosuppressive mechanisms in osteoblast cells of animals. In addition, certain viruses incorporate plasmin into a maturation step of their life cycle. For example, influenza viruses require plasmin to cleave a viral coat protein in order for the viral particle to become infectious.
Active plasmin is derived from an inactive precursor, plasminogen, which must bind through a lysine binding site to a cell or tissue before it can be transformed into plasmin. Synthetic antifibrinolytic compounds have been shown to act as serine protease inhibitors by preventing the binding of plasminogen to tissue through a lysine binding site, thereby inhibiting the activation of plasmin from plasminogen. These serine protease inhibitors include epsilon-aminocaproic acid (EACA), trans-4-(aminomethyl) cyclohexanecarboxylic acid, and 4-aminomethylbenzoic acid, as well as derivatives thereof. Because they mimic the amino acid lysine in this mechanism of action, these compounds are often called lysine analogs.
The protective effect of protease inhibitors in virus-infected animals has been previously documented. For example, it has been found that an injection of protease inhibitors into mice and chickens, which were infected with lethal doses of influenza virus, prevented dissemination of the virus in the host organism. Zhirnov et al., Protective Effect of Protease Inhibitors in Influenza Virus Infected Animals, Archives of Virology 73, 263-272 (1982). In this study, it was shown that an injection of the lysine analog EACA, at the time of infection, greatly reduced the severity and duration of the viral infection.
Also, lysine analogs have been shown to exert an effect on the immune system of various organisms via a mechanism of action that is not completely understood. It has been shown that mice injected with a lysine analog and infected with influenza virus showed enhanced resistance to subsequent influenza virus reinfection without additional lysine analog injections. Lozitsky et al., Resistance of Mice to Reinfection After E-Aminocaproic Acid Treatment of Primary Influenza Virus Infection, Acta virol. 32, 117-122, 1988. This study concluded that EACA can stimulate the mechanisms of specific and non-specific antiviral protection of an organism.
Further, EACA has been parenterally administered in combination with an inactive influenza vaccine to enhance the protective action of the vaccine against influenza in mice. Lozitskii et al, Effectiveness of the Combined Use of an Inactivated Vaccine and a Proteolysis Inhibitor in the Prevention Of Experimental Influenza, Zh Mikrobiol Epidemiol Immunobiol (USSR) December 1985 (12) p. 49-53.
Other applications of serine protease inhibitors in the prevention and treatment of disease are revealed in additional scientific journal articles. In rats and mice, injections of lysine analogs reversed the immunosuppression associated with experimental acute pancreatitis and enhanced the survival of animals infected with staphylococci. (Chalyi, et al., Protease Inhibitors as Immunomodulators in Experimental Acute Pancreatitis and Staphylococcal Infection, Zh Mikrobiol Epidemiol Immunobiol (Russia), January-February 1993, p. 62-65.) Also, hamster lymphoid cells treated with a lysine analog (EACA) showed enhanced proliferation in culture. (Hart, et al., Effect of Protease Inhibitors On Mitogen Stimulation of Hamster Lymphoid Cells, Experimental Cell Research, 102(2):253-63, 1976 Oct. 15.) Further, the anticarcinogenic properties of orally administered EACA have been studied in rats. (Bespalov, et al., The Inhibiting Effect of Epsilon-Aminocaproic Acid on the Incidence of Induced Tumors of the Esophagus, Nervous System and Kidneys, Vopr Onkol (Russia), 1992 38(1), p. 69-74.
In addition to the scientific journal articles set forth above, the following United States patents disclose applications of lysine analogs in treatment methods:
U.S. Pat. No. 4,600,582 to Stevens et al. teaches that incorporation of certain lysine analogs into parenteral injections containing allergens reduces adverse allergic reactions caused by the allergens. The lysine analogs that Stevens discloses as being suitable include EACA and transexamic acid as well as derivatives of these compounds.
U.S. Pat. No. 3,692,904 to Tsutsumi teaches the use of lysine analogs to alleviate scours, which is a form of dysentery, in mammalian livestock. The lysine analogs employed in Tsutsumi's method include EACA, trans-4-(aminomethyl)cyclohexanecarboxylic acid, and 4-aminomethylbenzoic acid, as well as pharmaceutically acceptable salts of these compounds. This patent discloses that these lysine analogs can be administered intravenously by injection or orally by themselves or admixed with animal feed. Additionally, Tsutsumi states that these compounds can be used in combination with other medicaments commonly used for treatment of scours, including sulfa-drugs or antibiotics. While Tsutsumi's disclosure is directed primarily to the treatment of scours, this patent also teaches that the compounds may be used to prevent or reduce the frequency of scours when added to the animal feed on a regular basis.
The patent to Tsutsumi, however, does not specify the mechanism by which the lysine analogs treat or prevent scours. Likewise, Tsutsumi is silent as to any use for lysine analogues beyond treating a single specific disorder, scours, in domestic animals. Moreover, Tsutsumi does not teach or suggest administering lysine analogs to any animals other than mammals such as pigs (piglets), cows, sheep, horses (foals), and goats.